1. Field of the Invention
This invention relates generally to electronic throttle control position sensors and more specifically to such sensing devices that determine position as a function of sensed magnetic flux density.
2. Background Art
Position-sensing devices are well-known in the art. These range in sophistication from local mechanical repeaters to remote electronic analog and digital devices. Early methods used a system having a xe2x80x9clook-up table.xe2x80x9d This required a measured value to be xe2x80x9clooked up,xe2x80x9d electronically or mechanically, and converted to a desired value. Understandably, this method is too expensive, inaccurate and slow to find much application today.
An alternative and low-cost method for position sensing uses an incremental encoder. Limited resolution and the potential for loss of position information as a result of detrimental noise or temporary power loss severely limit its consideration for critical applications. Absolute digital encoder methods typically require a multiplicity of sensing elements at significant cost. Contacting types of sensing elements suffer from mechanical wear-related problems that can detrimentally affect signal integrity and device longevity.
More recent methods for position sensing have used devices that determine position as a function of magnetic flux density. Commercially producing a sufficiently accurate and precise analog sensor for use in determining physical positions in that manner has proved to be difficult. The effects of variations in input offset, input gain, temperature, output slope and output signal limiting placed severe constraints on the manufacturing of such sensing devices in an efficient and cost-effective manner using high-volume, automated techniques. Sensing devices made under these constraints tended to be either inaccurate and imprecise or costly or both.
The electronic position sensor for sensing the position of a movable member includes a magnetic flux sensor. The latter sensor preferably includes a programmable linear ratiometric Hall-effect integrated circuit that has programmable gain, offset voltage and temperature compensation. The invention also includes a magnet, which may be a permanent magnet or an electromagnet, to provide a defined magnetic field. A magnetic flux sensor is disposed proximate the magnet, forming a gap therebetween.
The magnetic flux sensor includes an electronic circuit having programmable ratiometry, gain, offset voltage and temperature compensation. Relative motion is initiated between the magnet and the magnetic flux sensor in response to movement of the movable member. The relationship between the position of the movable member and an electronic circuit output in response to magnetic characteristics sensed by the magnetic flux sensor results in a linear function between two defined points within a specific range of at least one magnetic flux density, the amplitude of an electronic circuit output signal representing movable member position.
The magnet is typically rotatable about an axis of rotation in response to movement of a movable member, which is typically an automobile accelerator pedal lever arm. The magnetic flux density between the magnet and the magnetic flux sensor is a function of the angular disposition of the magnet and thus of the movable member. The relationship between the magnetic flux density sensed by the magnetic flux sensor and the position of the movable member need only be linear or some specified geometric function between two defined points within a specific range of magnetic flux density. Usually, a linear overall transfer function is preferred for the sensed variation of magnetic flux density versus rotation or translation.
In some cases, nonlinear deviations of system parameters, such as the cross sectional area of a fuel tank versus depth, can be linearized by implementation of a corresponding and opposite sense nonlinear magnetic transfer function such that the resultant overall transfer function is linear. Mechanical linkages, cams, and the like can also produce nonlinearity in the relative motion of the magnetic component and the magnetic field sensing component of the invention. Likewise, nonlinear deviations due to various mechanical articulation components of the device can be compensated, and thus canceled, by implementation of an appropriate but opposite nonlinear magnetic transfer function resulting in the typically-desired overall linear transfer function for the device.
In a first preferred embodiment, the magnet is a permanent magnet that has a configuration of a circular plate of uniform thickness. The magnet is magnetized in an axial direction relative to the axis of rotation of the magnet, and the plane of the magnet is disposed at an oblique angle relative to the axis of rotation of the magnet. It is rotatably mounted so that it is spaced from the magnetic flux sensor in an axial direction relative to the axis of rotation of the magnet. A rotation of the magnet varies the gap between it and the magnetic flux sensor, thus varying the flux sensed by the magnetic flux sensor as a function of the angular disposition of the magnet.
In a second preferred embodiment, the magnet is typically a permanent magnet that has a configuration of a linear cam ring. The magnet is magnetized in a radial direction relative to the axis of rotation of the magnet. It is rotatably mounted so that it is spaced from the magnetic flux sensor in a radial direction relative to the axis of rotation of the magnet. A rotation of the magnet varies the gap between it and the magnetic flux sensor, thus varying the flux sensed by the magnetic flux sensor as a function of the angular disposition of the magnet.